Transistor keyer



July 20, 1965 L. J. M DONALD TRANSISTOR KEYER Filed April 26, 1961 tmh tM29 INVEN TOR Lye/l u! McDonald m qrw I V% W \G 5555.5.

10.2mm 2 m w m2 OP United States Patent 3,196,201 rnnnsrsroa nnvnn LyellJ. Mel-Donald, Ellrhart, Ind, asslgnor to C. G. Conn Ltd, Eikhart, Ind,a corporation of Indiana Filed Apr. 26, 1961, Ser. No. 105,697 11 laims.(Cl. 84-426) This invention relates to electronic musical instrumentsand more particularly to a keyer circuit for an electronic organ.

It is desired to achieve tones from an electronic organ which simulatetones from a pipe organ, including tones which start and stop slowly. inproviding a flute note for example, it is advantageous to have somemeans of controlling the build up and decay of the electronic signalreaching the output circuit of the organ. It will be understood that ifthe electronic signal is controlled by a simple on-oif switch, thesignal in the circuit following the switch changes from zero, or arelatively small value, to its maximum in an abrupt manner when theswitch is closed. The signal would similarly return to zero in an abruptmanner and very often, particularly with fiute notes, would produce anundesirable transient or pop at the start and stop of the tone.

It is therefore an object of the present invention to provide anelectronic organ keyer adapted to control the manner in which a tonestarts and stops, and to minimize undesired transients in the tonesignal.

Another object of the present invention is to provide a transistorizedkeyer adapted to generate long sustain notes from an electronic organ.

A further object of the present invention is to provide an electronicorgan having a plurality of individual keyers which are isolated fromeach other, and in addition provide a simple and inexpensive means forselecting one or more sustain intervals.

A feature of the present invention is the provision of an organ :eyercircuit including a transistor device and time constant bias circuit tocontrol the build up and decay of an oscillator signal passed by thekeyer circuit.

Another feature of the invention is the provision of a transistorizedkeyer circuit including a capacitor to retain and decrease the biasapplied to a transistor device gradually with time. Different blockingvoltages and impedances are selectively connected to the capacitor toaiford different graduations of sustain time.

A further feature of this invention is the provision of a keyer circuitincluding twelve transistorized keyers for one octave, having theirrespective collector electrodes connected together and supplied with adirect current operating voltage through one resistor.

Another feature of the present invention is the provision of atransistorized keyer circuit adapted to aid in accomplishing longsustained sounds from an electronic organ and including neon lamps toprovide isolation between keyers controlled by a single voltage to allowthe keyers to operate independently of one another.

A further feature of this invention is the provision of an organ keyerincluding a plurality of thermistors positioned about the transistorkeyer to offset variation in transistor operation occurring because ofchanges in room temperature and/or internal temperature of an electronicorgan.

In the accompanying drawing:

FIG. 1 is a schematic diagram of a simplified transistor keyer circuitof the present invention; and

FIG. 2 is a schematic diagram of a circuit including a plurality ofkeyer circuits of the present invention.

In accordance with the present invention, a transistorized signal keyeris provided for an electronic organ which controls the magnitude of asignal applied from a tone generator to the output circuit of the organ.The keyer therefore acts as a variable gain amplifier whose gain may becontrolled by application of the proper biasing current to the controlelectrode of the transistor. A blocking voltage of one polarity isprovided to the control electrode to prevent conduction between theinput and output electrodes. A key may be actuated to provide a voltageof the opposite polarity to override the blocking voltage and cause thetransistor to conduct. The transistor valve can be biased to permit verylittle or no signal to pass through the keyer, the actual ratio ofmaXimum-to-minimum signal output being about decibels. The bias currentwhich increases or decreases the keyer output may be controlled so thatit increases or decreases gradually with time, and therefore themagnitude of the oscillator signal at the keyer output circuits varieswith time in a generally similar manner to the controlled bias current.Sustain tones or intervals are provided by decreasing the transistorbias current very slowly by means of a capacitor coupled in the circuit,which may be governed in its operation by a switch actuated variableimpedance circuit path. When several keyers are connected together, aneon lamp is connected in the circuit to provide isolation betweenindividual keyers coupled to a single blocking voltage source, allowingthem to operate independently from one another, and at the same timepermit a simple, inexpensive means of selecting one or more sustainintervals. In addition a thermistor, which has a negative temperaturecoeflicient, may be connected to the circuit to otfset variations oftransistor operation occasioned by changes in temperature.

Referring now particularly to FIG. 1, the transistor keyer circuit ofthe present invention is used to control the application of input signalvoltage from a tone generator, generally indicated at the referencenumber 10, to an output circuit. The tone generator 10 includes tube 11connected to an oscillator tank circuit 12 comprising an inductor 14 anda capacitor 16. The tube 11 is energized by a positive potential of 36volts. Signals from the tone generator it? are applied through resistor18 and across resistor Ztl to the emitter electrode 23 of transistor 22.Such signals are applied through the tran sister 22 to the collectorelectrode 25 and to the output circuit connected thereto when thetransistor 22 conducts.

The transistor 22 is of the PNP type and is controlled by the voltageapplied to the base electrode 24 thereof. The collector electrode oftransistor 22 is connected to a 6 volt supply by resistor 46. Thetransistor is normally non-conducting as a positive blocking voltage isdeveloped across resistor 32 from source 26 through resistors 28 and 3%,to provide a sufiicient base to emitter positive bias voltage to holdtransistor 22 non-conducting. A source of negative keying voltage 34 isconnected to one terminal of key 36, and when the key is closed thispotential is applied through resistors 40 and 30 across be e resistor 32to provide a negative voltage on the 1: base of transistor 22 to causethe transistor to conduct. This condition continues as long as key 36 isclosed, and a charge is stored on capacitor 42 when the key 36 is closedto hold the transistor 22 in conduction after the key is released.Capacitor 42 discharges through resistors 30 and 32 and through resistor28, to reduce the negative voltage at the base 24 of transistor 22, andthe capacitor charges in a positive direction from the positive source2.6. The voltage from source 26 is effective to discharge the negativevoltage across capacitor 42 and to provide a positive charge thereacrossto hold the transister 22 cut ofi.

It may be desired to control the period after which key 36 is open thatthe tone continues to provide what is known as sustain action. This maybe accomplished through action of switch 44 which controls the positiveblocking voltage applied to the base of transistor 22. When the switch41 applies a smaller positive voltage, it will require a longer time forthe negative voltage on capacitor 30 to be neutralized to cut oiltransistor 20. This will provide a longer sustain action.

In operation, when the key 36 is open, a positive voltage is applied tothe base of transistor 22 and the emitter current of the transistor isessentially zero. With the key in this position, blocking voltage source26 supplies a current through resistors 28, 30 and 32 which provides apositive voltage at the base of transistor 22 which holds the same cutoil'.

With the key 36 open, the polarity of the ungrounded terminal of thecapacitor 4-2 is positive. When the key 36 is closed, the polarity ofthe charge on capacitor #32 reverses and acts to change the base biascurrent. The negative charge on capacitor 42 controls the base biascurrent, and consequently the degree to which the keyer is turned on.Resistor 4d governs the rate at which the charge builds up across thecapacitor 42 and this controls the signal build-up in the keyer outputcircuit. It will be understood that the transistor collector current isa function of the base bias current over the collector current range.When the collector current reaches a saturation value, all but a fewtenths of the collector supply voltage is developed across the collectordirect current load resistor 4-6. After the collector current reachessaturation, it is essentially unchanged as the base bias currentcontinues to increase.

In the output circuit 56 of the keyer transistor 22, the capacitor 49 isused to reduce the short duration components of the transient signalthat appears in the collector circuit due to the collector currentchanging when the keyer is turned on. A second capacitor 5%) andresistor 52 form a filter section which reduces the long durationtransient, which might be considered a low frequency component of thetransient. Resistor 54 isolates the keyer from other circuits connectedtogether to provide the complete organ output.

The relatively high dynamic resistance of the transistor collectorcompared to the collector load resistance 4-6 permits combining severalkeyers (FIG. 2) in a single circuit with relatively slight attenuationof any signal. The plurality of keyers may be connected together andsupplied with a DO operating voltage through one resistor. When thecollector currents of all the open keyers are substantially belowsaturation, the collector current of the one transistor is essentiallyindependent of the collector current of any other open or closed keyer.Therefore, the total current flowing through resistor 46 will beproportional to the number of keyers that are simultaneously open. Thisassumes all transistors in a particular octave are alike.

FIG. 2 shows a circuit including a plurality of keyers 69 and 7d,generally like the keyer of FIG. 1, connected together. Like componentsare identified by like numerals. The outputs of the keyers 60 and 70 areshown fed to an amplifier and tone filter 80. The sustain or blockingvoltage is controlled by a voltage regulating circuit indicated at 9dwhich performs a function comparable to that of switch 44 of FIG. 1 inthat it regulates the blocking voltage to the keyers, individually andseverally.

Voltage regulating circuit 9t which supplies the voltage to control thesustain action of the keyers 60 and 7t) includes an amplifier controltube 64 and a series regulator tube 62. It will be understood that thevarious voltages on the supply lines will be dependent upon the relativevalues of the circuit components utilized in the practice of theinvention. The plate of tube 64 is connected to the grid of tube 62 andfrom there to the 425 volt B+ line 67 through resistor 66. The controlgrid of the amplifier tube 64 returns to ground through a resistor 72.The cathode of tube 64 is connected to a positive potential of volts andthe second grid is connected to a positive potential of 170 volts.

Thermistors 7d are shown on the keyer side of the circuit and areconnected in parallel with resistor '72 to the control grid of theamplifier tube 64. The thermistors 74 operate in the known manner tocompensate for temperature rise, or drop, clue to the proximity of heatproducing assemblies in the organ as well as changes in the ambienttemperature. The temperature compensating effect of thermistors '74 isparticularly effective in causing the transistors to cut off at thedesired time. When the temperature increases the L, of the transistorincreases which increases the current through resistor 32 which tends tohold the transistor conducting. The 1 of the transistor is the currentthrough the collector-tobase junction when the emitter is open-circuitedand the collector-to-base junction is reverse biased. The thermistors"74 act to raise the blocking voltage on line 88 which counters theeffect of the increased 1 of the transistor. The thermistors 74 may bepositioned at various point along the keyer chassis and connectedtogether to function as one thermistor. The thermistors when used inmultiples and spread out, average the temperature that the keyersexperience from one part of the keyer section to another.

Switches 76 and 73, which are the equivalent of switch S4 of FIG. 1,control the blocking voltage applied to the keyers 6t) and 76 byselectively connecting the resistors Sit-81, til-33, or 34%5-5 in thecontrol circuit. Regardless of which path is chosen resistor 72 andthermistor 74 are in the circuit connected to the grid of tube 64. Theswitches 76 and '78 operate independently of one another and in additionto selecting the resistors in the control circuit, operate to make aconnection to line 36 connected to the neon tubes 94.

For a more thorough understanding of the operation of the circuit ofFIG. 2, it is pointed out that three control lines are connected to thetwo keyers including keys 98 and 169 respectively. These arerepresentative of a large number of keyers which may be so connected.The first line 86 is the neon bulb conduction line, the second line 558is the blocking voltage conduction line, and the third line 92 providesthe keying voltage. Keying voltage supply 89 is connected to the line92.

In operation, when the switches '76 and 73 are not operated and'contacts89 and 93 are open, resistors 84) and 81 are connected to the cathode oftube 62 and are in series with parallel resistor '72 and thermistor 7Resistors 80 and 81 control the voltage applied to the grid of controltube 64 to provide the desired voltage at the cathode of tube 62. Thisvoltage is applied to the blocking voltage line 88. With switch '78 inthe unoperated position'as shown, line 86 is connected to line 88through contacts 5 and neon bulb 94 bridges resistor 28 so thatresistors 23a, 3% and 32 are connected to the cathode of tube 62 throughthe neon lamp 94. This provides the potential on the capacitor 42 and onthe base of transistor 22 to provide the normal keying action.

When the key 93 (or 1%) is now operated a negative voltage from line 92is applied through resistors 4t), 3t

3 V and 32 to cause the transistor 22 to conduct as was described inconnection with FIG. 1. Capacitor 42 and resistor 40 control(essentially) the build up of the voltage at the base electrode tocontrol the attack characteristics of the tone and also controls thesustain and decay characteristics.

For short sustain action, the switch '78 is moved to its operatedposition and switch '76 remains as shown. The resistors 80 and 81 aredisconnected, since contacts 01 are open, and resistors 84 and 85 areconnected in series with resistors 72 and '74 through contacts 93.Resistors 34 and 85 are of a higher resistance value and therefore thevoltage applied to the grid of control tube 64 is less. This causes adecrease in plate current at tube 64 which in turn causes the platevoltage of tube 6 5 to rise and the grid voltage of tube 62 to rise withit since this plate and grid are directly connected. The voltage on thecathode of tube 62 will tend to follow the grid voltage and will risethereby increasing the blocking voltage on line 88. As switch 78 openscontacts 95, the neon bulb 94 is disconnected from line 83 and iseffectively out of the circuit. The discharge path from line 08 tocapacitor 42 is therefore through resistor 28 in series with resistor2811. As resistor is much larger than resistor 23a, the resistance ofthe discharge path is greatly increased. Although the voltage on line 88is increased, the resistance of the path to capacitor 42 is increased bya greater factor so that the discharge time for this capacitor isincreased. This causes the transistor 22 to conduct for a longer timeafter key 98 is released to increase the sustain time of the toneapplied to the lreyer.

When long sustain is desired switches 76 and 73 are both operated. Whenthe switches are in this position, resistors 8 and are disconnected andresistors 32 and 83 are connected to resistors '72 and 7d. Resistors 82and 83 have less resistance than resistors 34- and 85 so that thevoltage at the grid of tube 64- is more. This causes the voltage at thecathode of tube 62 to be less as previously described. Therefore theblocking voltage applied to the line is less, and the voltage applied tocapacitor 42 is less so that the discharge time is increased.

The neon lamps serve two important purposes in the operation of thekeyer circuit. First, they provide effective short circuits acrossresistors 28, as described above, so that the blocking voltage, droppedabout volts by the neon tube, is applied to resistor 28a to provide thenormal decay. When the neon bulb circuits are opened, the resistors 28are in the discharge paths and increase the resistance thereof greatlyto increase the sustain time. The second purpose of the neon lamps is toisolate the keyers so that each keyer can be operated by one simpleswitch. This switch (contacts 95 or" switch 2%) simultaneously changesthe sustain duration of one or more keyers, and at the same time permitsthe independent operation of each keyer.

If the switches 76 and '78 are operated for long sustain action and thekey 93 of one keyer is closed and the key 100 of another keyer is open,the voltage across the neon lamps 9d of the two keyers is not enough tocause these lamps to fire so that the keyers are isolated. However, ifthe switch 78 is operated and the switch '76 is not operated (i.e. shortsustain), and the keys 9% and 100 are in the same condition as describedabove, the voltage across neon lamps 94 may be enough to cause the lampsto fire. Accordingly, there is a path for the blocking voltage appliedto one keyer through the neon lamps 9 5 to the other keyers. Althoughthis will change the resistance of the path for the blocking voltage ofthe capacitor 42 of the keyer which is operated the effective timeconstant is not substantially changed. This is because the coupling ofthe keyers through the neon lamps ties together the capacitors andresistors of the keyers which are coupled to increase the capacity anddecrease the resistance by the same factor, which is governed by thenumber of keyers which are intercoupled. Further the neon lamps, whenthey do fire, are fired for only a short time. The net eiiect of this isonly a minor change in the sustain time.

A chart of component values for the circuit of PEG. 2 appears below.These values are not intended to be critical to the practice of thepresent invention but are given as an example of the values which may beused in order that the detailed description will be complete.

Resistor 20 680 ohms. Transistor 2.2 Type 59625. Resistor 28 2.2megohms. Resistor 255a 120,000 ohms. Resistor 30 1.8 megohms. Resistor32 4700 ohms. Resistor d0 6800 ohms. Capacitor 42 1.35 microfarads.Resistor d6 12,000 ohms. Resistor 52 100,000 ohms. Resistor 5d 100,000ohms. Tube 62 Type 6EAS. Tube 64 Type 6EA8. Resistor 72 680,000 ohms.Resistor 390,000 ohms. Resistor til 250,000 ohms. Resistor $2 560,000ohms. Resistor 33 250,000 ohms. Resistor 84 1 megohm. Resistor 525500,000 ohms.

The invention provides therefore a transistor keyer circuit for anelectronic organ to control the magnitude of an oscillator tone signalthat reaches the output circuit of the keyer. The bias current whichcontrols the keyer output is controlled so that it increases ordecreases gradually with time thereby varying the oscillator signal inthe keyer output circuit in a similar manner. Variation of the sustaintime or interval is provided by changing the magnitude of the blockingvoltage applied to the base bias control circuit of the transistors ofthe keyer and/or by changing the release time constant of that controlcircuit. Several keyers may be connected together and means are providedin the present invention to effectively isolate the individual keyers.

I claim:

1. In an electronic organ including a tone generator for providing asignal corresponding to a musical tone, a keyer adapted to control theattack and decay of the tone including in combination, a transistorhaving input, output and control electrodes, means for applying thesignal from the tone generator to said input electrode, means connectedto said output electrode for deriving the signal therefrom, and acontrol circuit connected to said control electrode including blockingvoltage supply means for applying a first potential to said controlelectrode to prevent conduction between said input electrode and saidoutput electrode, said control circuit including switch means forcontrolling the amount of blocking voltage applied to said controlelectrode, said control circuit having means including a key forapplying a second potential to said control electrode to override saidfirst potential and cause said transistor to conduct, said last namedmeans including storage means for applying a portion of said secondpotential to said control electrode, with said portion graduallydiminishing after said key is released.

2. The structure of claim It wherein said storage means includescapacitor means, and said second potential charges said capacitor meansto provide a voltage at said control electrode to render said transistorconducting, with said capacitor means storing a potential to hold saidtransistor conducting to provide sustain action.

3. The structure of claim 1 wherein said storage means includescapacitor means and means forming a discharge path therefor, and saidsecond potential charges said capacitor means to apply a potential tosaid control electrode to render said transistor conducting, with saidfirst potential being continuously applied to said capacitor J means andacting to reduce the charge stored thereon by said second potential.

4. In an electronic organ including a plurality of tone generators forproviding signals corresponding to musical tones, and playing keys forcontrolling the tones, a keying system for controlling the attack anddecay of the tones including a plurality of keyers, each keyer includinga transistor having input, output and control electrodes, means applyingthe signal from a tone generator to each of said input electrodes, meanscoupled to said output electrodes for utilizing the signals therefrom,and a control circuit connected to each of said control electrodesincluding means for selectively applying a first potential to saidcontrol electrodes to hold said transistors nonconductive, each of saidkeyers including a switch coupled to a playing key for applying a secondpotential to said control electrode of'said transistor thereof tooverride said first potential and cause said transistor to conduct,whereby said transistors may be individually rendered conducting byoperation of the playing keys.

5. The keying system in accordance with claim 4 wherein said controlcircuit includes thermistor means for raising said first potentialapplied to said control electrodes of said keyers with increase intemperature.

6. A keying circuit for controlling the application of a plurality ofsignals from signal sources to an output circuit, and wherein the attackand decay of the signals are controlled, said circuit including aplurality of keyers, each keyer including a transistor having input,output and control electrodes, means for applying a signal to each ofsaid input electrodes, means coupled to said output electrodes forutilizing the signals therefrom, and a control circuit connected to eachof said control electrodes including means for applying a firstpotential to said control electrodes to hold said transistorsnon-conductive, each of said keyers including a key for applying asecond potential to said control electrode of said transistor thereof tooverride said first potential and cause said transistor to conduct,whereby said transistors may be individually rendered conducting byoperation of said keys of said keyers, each of said control circuitsincluding a neon lamp for applying said first potential to said controlelectrode of the transistor of each keyer and providing isolationbetween said keyers.

'7. A keying system for controlling the attack and decay of a pluralityof signals from sources including in combination, a plurality of keyerseach including a transistor having input, output and control electrodes,means for applying a signal to each of said input electrodes, meanscoupled to said output electrodes of each transistors for deriving asignal therefrom, a control circuit connected to said control electrodeof each transistor including resistor means and capacitor means, andvoltage supply means for applying a first potential of one polarity tosaid control circuits, said first potential being applied across saidcapacitor means of each control circuit to said control electrode of theassociated transistor to hold such transistor non-conducting, each ofsaid keyers including a key for applying a second potential of oppositepolarity to said control circuit to override said first potential andcause said transistor to conduct, said capacitor means charging to saidopposite polarity by said second potential whereby said transistorcontinues to conduct for a sustain interval after said key is released,said first potential discharging said capacitor means after said key isreleased and charging the same to said one polarity to cut oil saidtransistor, and switch means coupled to said voltage supply means forchanging said first potential to thereby change the duration of saidsustain interval, each of said control circuits including a neon bulbconnected to said resistor means thereof and to said switch means andrendered selectively conductive by said switch means to bridge at leasta portion of said resistor means to change the discharge time of saidcapacitor means of the control circuit, said neon bulbs of said controlcircuits further operating to suhstantially isolate said keyers from oneanother to allow said keyers to operate independently.

8. A keying system in accordance with claim 7 wherein said voltagesupply means includes voltage regulator means having thermistor meansfor raising said first poten tial with increase in temperature totemperature compensate said keyers.

E A keying system for controlling the application of signals from aplurality of signal sources to an output circuit, and for selectivelysustaining the applied signals, said system including in combination, aplurality of transistor keying devices each having input, output andcontrol electrodes, means for applying signals from the sourcesindividually to said input electrodes of said keying devices, meanscoupled to said output electrodes of said keying devices for utilizingthe signals therefrom, a plurality of control circuits individuallyconnected to said control electrodes of said keying devices, each ofsaid control circuits including capacitor means and means including aneon lamp for applying a first potential to said capacitor means tocharge the same to provide a bias at said control electrode of theassociated keying device to hold the same non-conductive, a key switchcoupled to each control circuit for applying to said capacitor means asecond potential of opposite polarity to said first potential to chargesaid capacitor means to provide a bias at said control electrode of theassociated keying device to cause the same to conduct, whereby each ofsaid keying devices is individually rendered conducting by operation ofthe associated key switch and is cut off in response to said firstpotential upon release of said key switch, and single switch meanscoupled to said plurality of control circuits for selectively completingthe potential applying circuits through said neon lamps, said switchmeans being operative to open the circuit through said neon lamps andthereby sustain the signal applied through a conducting keyer.

10. A keying system for controlling the application of signals from aplurality of signal sources to an output circuit, and for sustaining theapplied signals, said system includingin combination, a plurality ofsemiconductor keying devices each having input and output electrodes,

means for applying signals from the sources individually to said inputelectrodes, means coupled to said output electrodes for utilizing thesignals therefrom, a plurality of control circuits individuallyconnected to said keying devices for controlling the conduction thereof,each of said control circuits including capacitor means and meansincluding a neon lamp for applying a first potential to said capacitormeans to charge the same to a potential to hold the associated keyingdevice non-conducting, a key switch individually coupled to each controlcircuit for applying to said capacitor means thereof a second potentialof opposite polarity to said first potential to charge said capacitormeans to a potential to cause said keying device to conduct, wherebyeach of said keying devices is individually rendered conducting byoperation of the associated key switch and is cut oil in response tosaid first potential upon release of said key switch, and single switchmeans coupled to said plurality of control circuits for selectivelyapplying a potential to said neon lamps for application thereby to saidcapacitor means, said switch means being operative to remove thepotential from said neon lamps and thereby delay the cut off of aconducting keying device, so that the signal applied therethrough issustained.

11. A keying system for controlling the application of signals from aplurality of signal'sources to an output circuit, and for sustaining theapplied signals, said system including in combination, a plurality ofkeyers each having input and output terminals, means for applyingsignals from the sources individually to said input terminals, meanscoupled to said output terminals for utilizing the signals therefrom, aplurality of control circuits individually connected to said keyers,each of said control circuits including a neon lamp for applying a firstpotential to the associated lteyer to hold said keyer non-conducting, akey switch coupled to each control circuit for applying thereto a secondpotential of opposite polarity to said first potential to override saidfirst potential and cause the associated keyer to conduct, whereby eachof said keyers is individually rendered conducting by operation of theassociated key switch and is cut off in response to said first potentialupon release of said key switch, and single switch means coupled to saidplurality of control circuits for selectively completing the potentialapplying circuits through said neon lamps, said switch means beingoperative to open the circuit through said neon lamps and therebysustain the signal applied through a conducting keyer.

References (lifted by the Examiner UNITED STATES PATENTS 2,483,823 10/49George 841.26 2,811,669 10/57 Faulkner 84-161 2,811,887 11/57 Andersonet al. 84-l.23 2,885,573 5/59 Clapper 3fi7-88.5

2,906,959 9/59 Peterson.

OTHER REFERENCES Army Thin-690, Basic Theory and Application ofTransistors, March 1959, pp. 9091.

GEORGE N. WESTBY, Primary Examiner.

15 ARNOLD RUEGG, Examiner.

1. IN AN ELECTRONIC ORGAN INCLUDING A TONE GENERATOR FOR PROVIDING ASIGNAL CORRESPONDING TO A MUSICAL TONE, A KEYER ADAPTED TO CONTROL THEATTACK AND DECAY OF THE TONE INCLUDING IN COMBINATION, A TRANSISTORHAVING INPUT, OUTPUT AND CONTROL ELECTRODES, MEANS FOR APPLYING THESIGNAL FROM THE TONE GENERATOR TO SAID INPUT ELECTRODE, MEANS CONNECTEDTO SAID OUTPUT ELECTRODE FOR DERIVING THE SIGNAL THEREFROM, AND ACONTROL CIRCUIT CONNECTED TO SAID CONTROL ELECTRODE INCLUDING BLOCKINGVOLTAGE SUPPLY MEANS FOR APPLYING A FIRST POTENTIAL TO SAID CONTROLELECTRODE TO PREVENT CONDUCTION BETWEEN SAID INPUT ELECTRODE AND SAIDOUTPUT ELECTRODE, SAID CONTROL CIRCUIT INCLUDING SWITCH MEANS FORCONTROLLING THE AMOUNT OF BLOCKING VOLTAGE APPLIED TO SAID CONTROLELECTRODE, SAID CONROL CIRCUIT HAVING MEANS INCLUDING A KEY FOR APPLYINGA SECOND POTENTIAL TO SAID CONTROL ELECTRODE TO OVERRIDE SAID FIRSTPOTENTIAL AND CAUSE SAID TRANSISTOR TO CONDUCT, SAID LAST NAMED MEANSINCLUDING STORAGE MEANS FOR APPLYING A PORTION OF SAID SECOND POTENTIALTO SAID CONTROL ELECTRODE, WITH SAID PORTION GRADUALLY DIMINISHING AFTERSAID KEY IS RELEASED.